North Sea emergency response tugboat Nordic has a remarkable ability to move in close to an oil tanker or a liquid natural gas carrier leaking toxic and flammable gas in order to fight any fire and take the stricken vessel in tow. Nordic has been strategically stationed by the German authorities on the North Sea coast, ready, willing and able to cope with that sort of eventuality since early 2011.

In an environment heavily contaminated with gas the crew would be encapsulated safely in the tugboat’s air-sealed superstructure stronghold to breathe from an eight-hour supply of oxygen; all the while, ingeniously gas-protected MTU (Tognum subsidiary MTU Friedrichshafen) diesel engines would continue to pound away down below decks.

North Sea Rescue Tugboat Nordic:Photo credit – Pedwiki

Gas-protected MTU Diesel Engines

Nordic’s main propulsion engines are two specially equipped 20-cylinder MTU Series 8000 diesel engines rated at 17,200 kW, while two MTU type 12V 4000 M50A diesel generators are capable of meeting electrical needs as high as 2,280 kW.

Surprisingly, MTU found that a comparatively large amount of combustible gas entering the engines through the air intake is quite acceptable. The permissible amount of gas varies according to power output; for example, if less than 1,800 kW is produced then as much as 70% of the fuel in the combustion chamber can be gas. However, if the proportion of gas to diesel fuel becomes too high then of course the engine will auto-shutdown to avoid running out of control.

Temperatures are continuously monitored by MTU’s integrated ‘Callosum’ electronic control system when operating in ‘gas-safe’ mode (power automatically reduced to a maximum 4,000 kW) so as not to exceed a cylinder intake air temperature of 135C; MTU say that self-ignition of the gas/air mixture is extremely unlikely below that temperature. Flame barriers are also fitted in the air intake ducts to prevent burn-back.

Automatic cooling of exhaust gas by water spray in order to avoid triggering an external explosion is an additional safety measure when the tugboat is operating in a gas contaminated atmosphere.

Engine Modification Approval and Testing

Propulsion system specialists at MTU were advised during development by the German Federal Institute of Physics and Metrology, which tested the engine components – flame barriers and air intake system amongst others – for their efficient operation. Classification society GL then finally approved the engines for operation in any area where intake air is contaminated with external gases.

Notably at one point in the testing process, flammable gas was fed into the 8000-series diesel engine air intake system in an experiment conducted (understandably) under the supervision of the fire brigade, and outside working hours, on the MTU Friedrichshafen factory grounds.